1. Field of the Invention
The present invention relates to an electronic musical instrument which is adapted to prevent, when keys of the same note are depressed on upper, lower and pedal keyboards the generation of, a composite waveform produced according to the timing of the key depression on the keyboards, to cause a change in the volume of the musical sound being produced and thus, creating a disagreeable feeling.
2. Description of the Prior Art
In conventional electronic musical instruments, when keys of the same note are depressed on upper, lower and pedal keyboards, for instance, when keys of a note C.sub.4 are depressed on the upper and lower keyboards at different timing, the resulting composite waveforms widely differ according to the timing of key depression as shown in FIGS. 1(a) and (b). FIG. 1(a) shows the case where both musical waveforms produced by the key depression on the upper and lower keyboards have no phase difference therebetween, and FIG. 1(b) the case where they are phased 180.degree. apart. In practice, the composite waveform varies at random according to the actual timing of the key depression. Comparison of the composite waveforms in both cases of FIGS. 1(a) and (b) indicates that, in the former case, the volume is doubled after depressing the key of the note C.sub.4 on the lower keyboard (after a time t.sub.a), whereas, in the latter case, the volume becomes zero (after a time t.sub.b). Accordingly, the player feels unpleasant because the volume varies according to the timing of depressing his or her the keys of the same note on the different keyboards.
As a solution to this problem, there has been proposed, for example, in Japanese Pat. Pub. No. 41499/79 an electronic musical instrument provided with a phasing circuit for retaining musical waveforms in a fixed phase relation so as to prevent the volume of the composite musical sound from varying according to the timing of individual key depressions, but the phasing circuit used is complex in construction. Also there has been proposed, for instance, in U.S. Pat. No. 3,882,751, an electronic musical instrument of the type producing musical waveform signals slightly different in pitch between individual keyboards. For instance, in such a case as of a melody being played on the upper keyboard and a chord on the lower keyboard, their musical notes are produced at subtly different pitches. Furthermore, for example, when a key of a note C.sub.4 is depressed on the upper keyboard and a key of a note C.sub.3 on the lower keyboard, their musical sounds are produced at pitches which are not spaced exactly one octave apart but have a difference slightly smaller or larger than one octave. This serves to make unnoticeable the variations in the volume caused by the difference in the timing of the key depression. That is to say, when keys of the same note are depressed on different keyboards, musical sounds of subtly different pitches are combined, by which a beat is generated to thereby eliminate the defect that the volume varies according to the timing of the key depression.
However, the electronic musical instrument set forth in the abovesaid U.S. Pat. No. 3,882,751 has the following shortcoming: Namely, one of the two keyboards is set so that its musical sounds are produced at standard pitches, whereas the other keyboard is set so that its musical sounds are produced at pitches slightly different from the standard ones. Accordingly, when keys of the latter keyboard are depressed independently of the former keyboard, musical sounds are generated at pitches a little higher or lower than the standard pitches.
Moreover, keys of different notes are often depressed on different keyboards in actual playing, in which case, according to this conventional electronic musical instrument musical waveforms of slightly different pitches are produced, resulting in the defect that musical sounds of standard and nonstandard pitches are mixed. This rouses an inharmonious feeling in a person who has an acute sense of hearing. In other words, the generation of musical sounds of slightly different pitches gives an impression that a melody and a chord are inharmonious with each other.